1. Field of the Disclosure
Embodiments disclosed herein relate generally to the use of threaded unions, particularly so-called “hammer unions.” More specifically, the current disclosure relates to apparatus and method for locking threaded unions in a made-up condition, especially hammer unions subject to vibration or impacts, or which are located in inaccessible areas.
2. Background Art
Threaded unions, particularly “hammer” unions, are commonly used in petroleum exploration and production to join conduits together, for example, conduits carrying high-pressure fluids such as drilling mud, fracturing fluids, and oil and gas produced incidental to drilling activities. Hammer unions are generally considered to be economical, simple, reliable, and robust, and very easy to make-up and break-out quickly. Examples of hammer unions include, but are not limited to, the WECO® brand hammer unions available from FMC Technologies of Houston, Tex.
Typically, hammer unions are used in more temporary situations, such as joining together sections of joints (e.g., Chicksan® joints) used for pumping fracturing fluids into a wellbore under high pressure. In these applications, hammer unions rarely loosen (or “back-off”) in service because the duration of the application is so short. However, hammer-unions may also be used in certain long-term applications for their ease of make-up and break-out, especially, for example, for equipment that may need to be replaced quickly and efficiently (e.g., rotary hoses for conveying drilling mud between a stand-pipe manifold and a rotary swivel or top drive, or components of a choke manifold, such as valves, chokes and spools, which may fail unexpectedly due to erosive flows). In these longer-term applications, there may be a need to ensure that the hammer union does not loosen during service.
Several locking mechanisms for threaded unions are described in the prior art, for example: U.S. Pat. No. 4,501,521, disclosing a castellated locking fastener assembly, U.S. Pat. No. 6,139,068, disclosing a union lock for maintaining a union between two conduits, and U.S. Pat. Nos. 7,258,372 and 7,201,404 (by the same inventor) disclosing a union nut with lock members. Locking mechanisms for quick-disconnect fittings are also known in the prior art, for example, U.S. Pat. No. 5,374,085, which discloses a mechanical locking device for use with conventional quick-disconnect fluid couplings.
Hammer unions typically include three major parts: a shouldered nipple, a union nut, and a threaded nipple. The hammer union is typically made-up and broken-out by applying a sledge hammer to radial lugs on the union nut. Refer now to FIG. 1A, a cross-sectional view of a conventionally made-up hammer union with a spherical metal-to-metal pressure seal is shown. Other types of pressure seals are possible, including those having elastomeric or composite seals, especially for (relatively) low working-pressure unions. Union nut 1 has hammer lugs 1A, internal threads 1B and flat surface 1C. Union nut 1 bears on shoulder 2A on a distal end of shouldered nipple 2, which also has sealing surface 2C and outer diameter 5. Threaded nipple 3 has external threads 3A and sealing surface 3B.
FIG. 1B shows a perspective view of a hammer union with an external shoulder, which in this example is a hose ferrule for attaching the union to high pressure flexible hose. The hammer union comprises union nut 1 with hammer lugs 1A and flat surface 1C, shouldered nipple 2, and threaded nipple 3. In this example, which is typical of many applications on drilling rigs, shouldered nipple 2 has an enlarged section 2D (in this example, a hose ferrule) with transition profile 2E and external shoulder 2F. Transition profile 2E may be a constant or variable radius fillet or a chamfer, or another profile known in the art. Below union nut 1, shouldered nipple 2 has outer diameter 5. In the made-up condition, union nut 1 is separated from shoulder 2F by offset distance 4, which is typically designed to allow union nut 1 to drop down, exposing sealing surface 2C of shouldered nipple 2 (shown in FIG. 1A) so that it may be cleaned and inspected.
Other prior-art hammer union configurations include a union nut separated by an offset distance from an external shoulder, including valve bodies, hydraulic wyes, crosses and manifolds. Still other prior-art hammer union configurations may include a union nut separated by an offset distance from a small external shoulder or groove, while other prior-art hammer union configurations may include a shouldered nipple with a constant external diameter, that is, without external shoulders or grooves. Accordingly, there exists a need for a locking mechanism for a threaded union in a made-up condition that may be quickly installed on existing threaded unions.